Spatial and temporal analysis of the sand dynamics in alpine rivers for 3D numerical modelling

Hydraulic structures can impact the sediment continuity of the river and can create a sediment imbalance downstream of dams according to the different sediment classes (silt, sand, gravel). For operators, one important issue is the presence of sand (d>63 µm), which can lead to exploitation difficulties, issues for flushing or emptying operations as well as to ecological, industrial or safety issues. It was recognized that the percentage of sand particles that is trans ported by suspension compared to bedload transport can often prevail. However, today it is still a real challenge to evaluate the spatial and temporal variability of these sand concentrations in gravel-bed rivers since sand dynamics are generally supply limited. Using 3D hydro-sedimentary modelling could help to better understand processes of sand transport in rivers. In this article, we will present results from experimental monitoring that will then be used for 3D numerical modelling (TELEMAC 3D + Gaia) on engineered rivers in the Northern French Alps.